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Man undergoing biofeedback therapy, showing him lying connected to electrodes, studying the glow of an electric light bulb. Biofeedback is a technique whereby an auditory or visual stimulus follows on from a physiological response. For example, electrodes might be used to measure the subject's pulse rate with any variation represented by changes in the brightness of the light; this may allow him to control his heart rate by distinguishing between different intensities. How the technique works is unclear, but it is claimed that it can control pulse rate & blood pressure, relax spastic muscles and also control migraine (severe headache) attacks.